U.S. Steel Corp. operates the Minntac Taconite processing facility near the city of Mountain Iron, where it produces taconite pellets that are shipped for use at steel mills.
Minntac operates under existing air quality and industrial wastewater permits.
Our role
The Minnesota Pollution Control Agency is committed to protecting human health and the environment and supporting sustainable job growth in the state.
The MPCA is responsible for issuing and enforcing permits that limit emissions and discharges from Minntac’s operations to protect the environment and health of Minnesotans. Those permits reflect current state law and regulations.
The MPCA issued the facility’s existing air permit in 2003, which covers the mining area, processing facility, and tailings basin. The permit expired in 2008 and is still current under an administrative extension. U.S. Steel submitted an application for an updated air permit in 2013. The MPCA issued a major amendment to the air permit in 2013.
The MPCA issued two wastewater permits for the facility, one for the mine site in 2003 and one for the tailings basin site in 2018.
The MPCA is in the process of re-issuing both air and wastewater permits for the facility.
Draft wastewater permit
The draft wastewater permit for the U.S. Steel Minntac facility's tailings basin is available for public comment from Aug. 26 to Oct. 12, 2026. Visit the posting in EngagementHQ to review the draft permit and supporting documents and to provide feedback.
Project information
Minntac has operated as a taconite processing facility near the city of Mountain Iron since 1967. The facility consists of the Minntac plant and nearby tailings basin.
Air
The processing plant currently uses wet scrubbers to control emissions from ore handling equipment. U.S. Steel has submitted a permit application to replace those wet scrubbers with dry cartridge filters to reduce particulate matter emissions. The draft permit would also require U.S. Steel to comply with updated taconite MACT standards and complete a National Ambient Air Quality Standards (NAAQS) compliance demonstration. The public comment period on the draft air permit closed on June 22, 2026. MPCA staff are currently reviewing comments.
Water
The MPCA has drafted an updated wastewater permit for U.S. Steel’s Minntac tailings basin. The permit covers the Minntac tailings basin, wastewater disposal systems, and surrounding landscape, an area of approximately 8,700 acres.
The draft permit makes the following significant changes from the previous permit:
- determination that seepage from the tailings basin is functionally equivalent to a direct discharge to surface water
- addition of interim and final sulfate limits for surface water and groundwater, including 41.4 mg/L in the Dark River, 10 mg/L in Little Sandy Lake, and 250 mg/L in groundwater at the property boundary
- a compliance schedule to meet interim and final limits for sulfate that accounts for the construction of a wastewater treatment facility on the west side of the tailings basin and a cutoff wall and groundwater treatment technology on the east side of the tailings basin
- addition of a total phosphorous limit to protect against harmful algae blooms in downstream waters
- addition of 10 new groundwater monitoring stations and three new surface water monitoring stations
Next steps and timeline
The public comment period on the draft air permit closed on June 22, 2026. MPCA staff are currently reviewing comments.
The draft wastewater permit for the tailings basin site will be available for public comment from Aug. 26 to Oct. 12, 2026. A public meeting to discuss the draft wastewater permit will take place from 6-7:30 p.m. on Sept. 29 at Iron Trail Motors Event Center in Virginia, Minnesota.